Piston



Jan. 7, 1930. M, TIBBET S 1,742,452

PISTON Filed June 12, 1926 Brae ATTOENEK Patented Jan. 7, 1930 HILTONTIIBBETTS, OF DETROIT,

MICHIGAN, ASSIGNOR T0 PACKARD MOTOR CAR COM- PM, 01 DETROIT, MICHIGAfi,A. CORPORATION 01 MICHIGAN PISTON Application filed June 12, 1926;Seriallio. 115,427.

My invention relates to devices for compensating for dimensional changes1n mechanical elements and due to expansion or contraction resultingfrom temperature variation, to which such an element jected.

The general object of the invention is to 7 control or modifysuchchanges soas to maintain certain of the dimensions of the elementsubstantially in a state of constancy or mainm tain a predeterminedrelationship between I the degree of frictional resistance between thesuch an element and a cooperating element.

A particular object is to provide a piston for an internal combustionengine whose diameter will remain substantially constant One method,heretofore, of attempting to overcome this'piston difliculty has been byproviding a split skirt for the pistonso that it would automaticallyspring inwardly when subjected to increased temperature, and whenpressed by the cylinder walls, and automatically spring outwardly whensubjected to decreased temperature and released by said cylinder wall,under the theory that a substan.

tially constant diameter of the piston would thus be maintained and aproper fit secured under all variations of temperature to which thepiston would be .subjected.

However, in some cases it has been found that pistons constructed asjust described, and partlcularly-when made of aluminum, contract andchange their diameter to such an extent as to become, when cold, looseand hence noisy. It will-be apparent; also, that piston and cylinderwill vary materially by changes in the temperature, and especially inthe case of an aluminum piston and iron cylinder, even though it mightnot be noisily loose when-cold.

In carrying out the principles of my inven-' tion, I provide themechanical element with athermally operated device which when subjectedto variations of temperature produces a force resulting in motion whichis trans-' mitted to the element and caused to oppose the force whichwould produce movement in may be sub-- under the conditions of varyingtemperature provide the skirt of the latterwith a longitudinal slot sothat such skirt .is normally capable of circumferential dimensional ex--pansion or contraction independently of tem- In applying such principleto a piston, I

perature variation. To the skirt I connect a thermally actuated d viceand in such a manner that a variation f temperature will effect. amovement in the device, which is transmitted to the skirt wall'and in adirection such as will decrease the diameter of the skirt in case itexpands or maintain the diameter in case it tends to expand and increasethe diameter in case it contracts or maintain its diameter in case ittends to contract.

The said invention therefore consists of means hereinafter fullydescribed and particularly pointed out in the claims.

The annexed drawing and the following description set forth in ple of myinvention may be employed.

. In said annexed drawing:

Figure 1 represents an axial section of apiston embodying my invention.

Fig. 2 represents a transverse section taken indicated by line vII----IIIn the illustrated embodimentof my invention, the piston l is,p,rovidedwith a head 2 and a; skirt 3 integral with or joined to the head, theskirt and head being separated at the wall portions thereof by acircumferential slot 4 extending completelyaround the periphery of thepiston 1, as'shown in Figure detail certain means for carrying out myinvention, the disclosed means, however, constituting but two of the avarious mechanical forms in which the princi- 1. 'The skirt wall isintersected by a slot 5 extending longitudinally from top to-bottom ofsame, and is shown in the drawing to be in clined with reference to thepistons axis.

As thus far described, the piston is of a construction heretofore knownand does not constitute any part of my invention;

- duce its It will be observed, however, that'the piston so constructedpermits the skirt normally to be subjected to a dimensional changeindependently of temperature variation and also is sub ect to suchchange as a result of such variation. By this I mean, that an exteriormechanical compressive force may be applied to the dismounted skirttorediameter and thereby contract the slot 5, or an expansive forceapplied to increase such diameter and enlarge the slot. Also that whensubjected to increased temperature its diameterwill be increased and thecircumferential extent of the metal also increased, while the slot isalso somewhat enlarged.

The above-construction is, however, in the form of my invention shown inFigs. 1 and 2, modified by providing additional metal upon the interiorof the wall of the skirt in the form of bead-like additions 6-6,respectively immediately adjacent the slot 5, and in these beads arerespectively embedded and fixedly secured, as forexample by casting, theends of a thermally-actuated loop-formed device 7 consisting of two flatsuperposed pieces of metal having ,diiferent co-eflicients of expansionasfor example steel and brass, that plate having the greatercoefiicientof expansion being located upon the outside of the loop. Asis well known, such a combination of metals when subjected to varyingtempera-- ture warps and produces or tends to produce motion in thedevice. In this case an increase of temperature will cause the ends ofthe approach or tend to approach and a loop to decrease would cause sameto recede or tendto recede from eachother, and in either case may beused to transmit force to the wall of the skirt adjacent to theslot. Theforce thus applied by the loop device 7 acts circumferentially of theskirt 3 andprovides a circumferential dimensional change therein whichis uniformly distributed about the circumference of the skirt. 1.

Such proportions and dimensions of the loop and its constituent partsand character of the metals are selected as will be necessary to producea movement of the loop ends, sufficient in its transmission to the s irtwall to counteract and equalize any expansive or contractive forcedeveloped interiorly of "the skirt metal and due to the variation oftemperature to which the piston is subjected in the operation of theengine, and the external diameter of the skirt will hence remainsubstantially constant for all temperatures, as

it will be understood that the amount of a movement produced by the loopwill vary substantially directly as the temperature.

Should it be found that it is also desirable to allow for theex ansionof the cylinder wall, the loop 'may force exerted upon the skirt wouldbe sufliciently less than an absolutely equalizing for example,

e designed so that the rather than completely equalized. In this wayallowance may be made for cylinder expansion and a constant relationshipsecured etween the friction surfaces of the piston and cylinder so as toeffect a constant frictional relation thereof for all the temperatures.

The proper design of the loop and proportioning of its parts may bedetermined empirically for any. given engine, set of operatingconditions, or character of piston, as will be apparentto those skilledin the art.

It will also be apparent to those skilled in the art that various formsof thermally operated devices may be used to accomplish the.above-described object, and I have illustrated. one such modification inFig. 3.

. In this latter instance, the device is generally flat with a centrallylocated bow 8, its

ends being fixedly secured in ribs 99 respectively and preferably nearthe skirt wall as shown,,so as totake advantage of; all the leverageossible. In this latter form the metal havmg the greater coefficient ofexpansion would be located inwardly, that is on the side of thedeviceadjacent the piston wall.

What I claim is:

1. The combination with a mechanical element normally,capable ofcircumferentially uniform dimensional changes independently oftemperature variation; of a thermally actuated device connected withsaid element and adapted to apply force thereto circumferentiallyopposed to that force tending to effect circumferential dimensionalchange in said element and due to temperature variation; whereby suchlast-mentioned change may be controlled.

2. The combination with a hollow cylindrical mechanical element normallycapable of circumferentially uniform dimensional changesindependently oftemperature variation; of a thermally actuated device cbnnected withsaid element and adapted to apply force thereto circumferentiallyopposed '7 to that force tending to effect circumferential dimensionalchange in said element and due to temperature variation; said devicebeing arranged so as to maintain a substantially constantcircumferentialdimension on the longitudinally extending slot and provided with athermally actuated device connected with the piston wall on 0 positesides of said slot, said device adapte to apply force to said oppositesides varying as its temperature. I

5. A hollow piston having a head, and a skirt formed with a longitudinalslot, the wall of said skirt being se arated from said head throughoutthe perip ery of the piston, said skirt being provided with a thermallyactuated device connected with the wall tion adjacent said slot andadapted under the influence of an increased temperature to apply a:torce to said wall portion tending to contract said slot.

6. A piston having a head, and a skirt formed with a longitudinal slot,thewall of said skirt being separated from said head; and a thermallyactuated device connected with said skirt and adapted, when subjected Yto an increased temperature, toexert on said sk1rt a force actinguniformly circumferentially and opposed to that force set up therein. bysuch increased temperature.

7. A piston having ahead, and a skirt formed with .a longitudinal slot,the wall of said skirt being separated from said head; and a thermallyactuated device connected with said skirt upon opposite sides of saidslot and adapted, when subjected to an increased temperature, to exerton said skirt aforce opposed to that force set up therein by suchincreased temperature.

8. A hollow piston having its wall formed with a slot and provided witha device comprised of two metals of difierent coeflicients of expansionand connected with said wall upon opposite sides of said slot andadapted upon thermal expansion to contract said slot.

9. A hollow piston having its wall formed with aslot and provided w1th adevice comprised of two super os'ed metal plates of dif-' ferentcoefiicients 0 expansion and connected with said wall upon oppositesides of said slot and adapted upon thermal expansion to contract saidslot. 7

10. A hollow piston having its wall formed with op osed beads and a slottherebetween, and a evi'ce comprised of two' superposed metal plates ofdifierent coeflicients of expansion and connected at its endsrespectively to the outer walls of said beads, the outer metalplate'having the greater coeflicient of expansion.

11. A piston having a head, and a skirt formed with a lon 'tudinal slotextending from its top to its ottom, thewall of said skirt beingseparated from said head; and a thermally actuated device connected withsaid skirt and. adapted, when subjected to an increased temperature, toexert on said skirt a force entirely opposed to-that force set uptherein by suc increased tem eratura 12. A piston having a hea and a Ipor- MILTON TIBBETTS. 7

